Recreational vehicles must be maintained in a level, horizontal position when parked in order to ensure comfort and proper operation of appliances, tables, and the like. Hydraulic and electric jacks exist to accomplish this task. These tend however to be both very expensive and difficult to install and operate.
For simpler levelling devices which are intended to fit under one or more of the vehicle's wheels, a variety of difficulties exist including providing complete height adjustability, bi-directional driving ability, and a functional, non-slip surface onto which the vehicle's tires can solidly mount and rest.